1. Field of the Invention
The present invention relates to adjustable air dielectric capacitors for electrical circuits. More particularly, the invention relates to an inexpensive miniature capacitor having an externally threaded concentric tube rotor which is biased toward and rotatably engages an internally threaded housing to rotate into and out of a fixed concentric tube stator.
2. Description of the Prior Art
Adjustable miniature air dielectric capacitors have been the subject of much inventive activity. One common type of capacitor has a rotor and a stator each in the form of concentric tubes, which intermesh. The stator tubes are secured at one end of an internally threaded housing. The externally threaded rotor rotatably engages the housing threads and is adjustable on the housing threads, into and out of the fixed stator (see U.S. Pat. No. 3,469,160). Capacitance is controlled by the amount of overlap between the concentric stator and rotor tubes.
Another type of capacitor also is provided with rotor and stator plates in the form of concentric tubes mounted within a housing. In accordance with this second type of capacitor, however, the rotor does not rotate while moving into and out of the stator. The nonrotating rotor movement is accomplished by a threaded drive screw upon which the rotor translates while guides on the rotor slide in longitudinal slots in the housing (see U.S. Pat. No. 3,483,450).
Regardless of the construction of an adjustable miniature air dielectric capacitor, there is an inherent need for positive electrical contact between the housing and the rotor and, in addition, for stable, constant rotor position with respect to the stator.